Exposure control apparatus

ABSTRACT

A multiple segmented photocell has its segments connected to a multichannel amplifier to which is also applied a reference signal representative to the total scene illumination and is operative to limit the output signal from any portion of the photocell which may result from a portion of the scene which has an inordinately high amount of illumination.

United States Patent [191 Harvey [45] Feb. 20, 1973 [54] EXPOSURECONTROL APPARATUS [75] Inventor: Donald Malcolm Harvey, Webster,

[7 3] Assignee: Eastman Kodak Company,

Rochester, NY.

[22] Filed: Feb. 22, 1972 211 Appl. No.: 227,968

[52] U.S. Cl. ..95/l0 CE, 95/10 C, 250/214 P, 356/222 [5 l] Int. Cl..G01j 1/44 [58] Field of Search..95/l0 C, 10 CE, 10 CT, 10 CD,

'II ll 3,563,143 2/1971 Petersen ..356/222 Primary Examiner-SamuelMatthews Assistant Examiner-Russel E. Adams, Jr.

Attorney-JV. H. J. Kline et al.

[ ABSTRACT A multiple segmented photocell has its segments connected toa multichannel amplifier to which is also applied a reference signalrepresentative to the total scene illumination and is operative to limitthe output signal from any portion of the photocell which may resultfrom a portion of the scene which has an inordinately high amount ofillumination.

5 Claims, 4 Drawing Figures MULTi-CHANNEL AMPLIFIER CIRCUIT ex'PosuRECONTROL SYSTEM v PAIENIEHrtazmm 3,717,077

as MULTI-CHANNEL r AMPLIFIER v FIG. 2

zv EXPOSURE CONTROL SYSTEM FIG. 4 our a b c d CHANNELS EXPOSURE CONTROLAPPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates generally to exposure control apparatus for aphotographic camera, and more particularly to exposure control apparatususing multiple light sensingmeans operative to establish the exposurecontrol signals for the camera.

2. Description of the Prior Art Generally in photography and inparticular in the socalled available light photography, dimly lit scenesmay include some form of an artificial light source which can createconsiderable exposure error when a conventional integrating photometricsystem is employed. It would be desirable that the exposure should bebased primarily on those portions of the subject which are normallyilluminated, but should substantially disregard those sources ofinordinately high illumination in the scene. Generally the sources ofillumination included within the field of a photometric system providethe major portion of the light intensity striking the photosensor withthe result being a general under exposure of the normally illuminatedsubject matter and a normal exposure of the source of illumination,which generally is an unsatisfactory overall result.

The above-described situation has long been recognized and variousattempts have been made to compensate for subjects having differingdegrees of brightness in a particular scene. For example, U.S. Pat. No.3,428,403 issued Feb. I8, 1969 to Masaichiro Konishi describes a systemusing a segmented photoresistor connected in series, with each of thesegments being exposed essentially to a different portion of the scenebeing photographed. Another U.S., Pat. No. 3,473,453 issued Oct. 21,1969 to Thomas Gross describes a photometric system using a plurality offour photoresistors connected in a series-parallel configuration to takeinto account portions of the scenes having different light intensities.While these systems have begun to compensate for portions of the scenehaving varying degrees of illumination, because of the serial connectionof at least two of the segmented photoresistors, they do not trulyisolate and consider individually each of the areas of the scene to bephotographed.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly it is a principalobject of the invention to provide an electronic exposure control systemwhich overcomes the disadvantages of the prior art.

Another object of the invention is to provide an electronic exposurecontrol system using a multiple photocell operative to independentlyevaluate various sectors of the scene to be photographed.

Yet another object of the invention is to provide an automatic exposurecontrol apparatus which effectively averages out or balances outportions of the scene having unduly high illumination therein.

The foregoing and other objects are accomplished according to one aspectof the invention wherein a segmented photocell has each portion thereofconnected in parallel to a summing and averaging circuit and to amultichannel amplifier. In the averaging circuit the gross detectedsignal is determined and then is divided by a predetermined value toyield a reference signal which is in turn applied to the amplifiercircuitry to effectively provide a maximum bias for each of the portionsof the signal from the segmented photocell. The outputs from theamplifier circuitry are in turn applied to a second summing circuit theoutput of which is applied to the electronic exposure control circuitryin a normal fashion. In this fashion, bright light spots are partiallybiased out to minimize this effect on the exposure control apparatus sothat the normally illuminated portions of the scene are notunder-exposed during the picture-taking process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic circuit diagram,partially in block, illustrating one aspect of the electronic exposurecontrol circuitry according to the present invention;

FIG. 2 is a schematic circuit diagram illustrating an alternativeversion of the electronic exposure control circuitry according to thepresent invention;

FIG. 3 is a graphical presentation of the gross signals derived from asegmented photocell; and

FIG. 4 is a graphical representation of the net signals applied to theexposure control apparatus, when utilizing control circuitry accordingto the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing and other objectsand advantagesof the present invention will become more readily apparentupon taking the following detailed description in conjunction with theabove-described drawings.

Referring first to FIG. 1, there is shown a multiple segmented photocell11 having segments 11a, 11b, 11c and lld. The light from a scene 10passes through a lens 12 to impinge upon the photocell 11. A battery orother source of energizing potential (not shown) is generally applied tothe segments of the photocell l1. Outputs from the individual sectionsof the photosensor 11 are applied in parallel to a summing circuit 13and also the same outputs are applied to a multichannel amplifier 1.5.The output 17 of the summing circuit 13 is applied across a firstresistor 19 and a second resistor 21 to ground, with the junction of thetwo resistors being applied to an additional input of the multichannelamplifier 16. A capacitor 23 is also connected between t the output 17of the summing circuit 13 and ground.

The output from a multichannel amplifier consists of an outputcorresponding to each one of the inputs from the photocell 1 1 and theseoutputs are applied in parallel to a second summing circuit 25, theoutput of which is applied in normal fashion to a typical exposurecontrol system or apparatus 27.

In operation, the outputs from the photocell 11 are applied to thesumming circuit 13 are operative therein to establish a gross signalfrom which a reference signal as determined by the amplification factorof the summing circuit 13 and the relative values of the resistors 19and 21 is derived. The reference signal is applied to the multichannelamplifier. The variable resistor 21 permits relative adjustment of thereference signal to be applied to the multichannel amplifier 21. Thesignal applied from the junction of the resistors 19 and 21 to themultichannel amplifier operates as a bias on each channel of theamplifier to set a maximum limit on the usable portion of the outputfrom each of the photocell sectors. Then the outputs from each channelof the multichannel amplifier are applied to the summing circuit 25,which combines the signals to provide the net signal to be applied tothe normal exposure control system of the camera.

As an alternate to the embodiment of FIG. 1, rather than using aseparate summing circuit to determine the reference voltage it would bepossible to use a second photocell 31 having its output connected acrossresisters 33 and 35 connected in series to ground with a junctionthereof applied to the multichannel amplifier 15. The second photocell31 in conjunction with its lens 36 is placed in a predetermined relationwith the primary photocell 11 to make sure that the same sceneillumination is being detected by each photocell so that the grossoutput of the photocell 31 is relative to the multiple outputs of thephotocell 11. The remaining operation of the apparatus of FIG. 2 is thesame as the operation of FIG. 1.

In order to better understand the operation of the circuitry of FIG. 1or FIG. 2, reference is made to FIGS. 3 and 4. FIG. 3 graphicallyrepresents what might be a typical output from each of the segments ofthe photosensor 11 of FIG. 1 or FIG. 2. In this particular illustration,it is assumed that a bright source of illumination such as the lamp 14of the scene in FIG. 1 impinges upon segment at of the photocell therebyresulting in an inordinately high output signal from this segment. Thesignals are applied to the summing circuit 13 to determine a grosssignal and are then divided down by the resistor divider network 19 and21, and a suitable bias applied to the multichannel amplifier whichlimits the output of each channel as indicated in FIG. 4. The referencelevel may be chosen as any reasonable fraction of the gross signaldepending upon the particular system requirements. As seen in FIG. 4,the voltage output from the multichannel amplifier is such that segmentsa and c are relatively unchanged, segment b is slightly diminished andsegment d is severly limited. These outputs are then applied to thesecond summing circuit 25 which provides the net signal to the exposurecontrol system.

While the foregoing represents what may be taken to be a preferredembodiment of the invention, it should be noted that the technique ofdetermining cutoff or reference voltage may include a system ofweighting the cutoff such-that its effect diminishes as the summed grosssignal increases. Thus, in scenes which are significantly brighter, itwould be inferred that the sources of illumination included within thescene have a less deleterious effect on the overall exposuredetermination period. Therefore at some point in the brightness scale,which would be determined by the system requirements, the primary sourceof light might be, for example, the sun and the cutoff level could bedisregarded altogether.

While the invention has been described generally as using a photocellsensing device, it will be apparent to those skilled in the art that anydevice capable of detecting varying amounts of light may be used. Also,while there has been shown a four segment photocell, it will be furtherapparent that any number of segments depending on design requirements orengineering preference may be used.

The invention has been described in detail with particular reference tothe preferred embodiments thereof, but it will be understood thatvariations and modifications can be affected within the spirit anclscope of the invention.

I claim:

1. For use in a camera having exposure control means, circuitryoperative to establish a control signal for the exposure control means,comprising:

a. light responsive means including a plurality of individual segmentsadapted to receive light from respective portions of a scene to bephotographed, each of the segments of said light responsive means havingan electrical parameter which varies in accordance with the intensity oflight incident thereon;

b. first circuit means containing a plurality of amplifiers, one foreach of said segments of said light responsive means, including meansfor connecting the output of each of said segments to a respective oneof said plurality of amplifiers;

. means for deriving a reference signal related in value to the totalscene illustration received by said light responsive means; and

d. means for applying a portion of said reference signal to each of saidchannels, operative thereby to selectively limit the output from each ofsaid amplifiers.

2. For use in a camera having exposure control means, circuitryoperative to establish a control signal for the exposure control means,comprising:

a. light responsive means including a plurality of individual segmentsadapted to receive light from respective portions of a scene to bephotographed, each of the segments of said light responsive means havingan electrical parameter which varies in accordance with the intensity oflight incident thereon;

. first circuit means operative to receive inputs from each of thesegments of said light responsive means and to provide an outputtherefrom as a single signal related to the sum of the individualportions;

. second circuit means containing a plurality of channels, one for eachof said segments of said light responsive means;

d. means for connecting each of said segments to a respective one ofsaid plurality of channels of said second circuit means;

means for applying a portion of the output from said first circuit meansto each of the channels of said second circuit means operative therebyto selectively limit the output from each of said channels; and f. meansadapted to receive the outputs from said second circuit means andprovide therefrom a net control signal to be applied to the exposurecontrol means.

3. The invention according to claim 2 wherein said first circuit meansis a summing amplifier.

4. The invention according to claim 2 wherein the means for deriving aportion of the output from said first circuit means to be applied tosaid multichannel amplifier comprises first and second resistorsconnected between the output of said first circuit means and a source ofreference potential, with the junction of said first and secondresistors applied to an input of said second circuit means;

5. For use in a camera having exposure control means, circuitryoperative to establish a control signal for the exposure control means,comprising:

a. light responsive means including a plurality of individual segmentsadapted to receive light from respective portions of a scene to bephotographed, each of the segments of said light responsive means havingan electrical parameter which varies in accordance with the intensity oflight incident thereon;

b. first circuit means containing a plurality of channels, one for eachof the segments of said light responsive means;

c. means for connecting each of the segments to a respective one of theplurality of channels of said first circuit means;

d. second light responsive means adapted to receive .'means for applyinga portion of the output from said second light responsive means to eachof the channels of said. first circuit means operative thereby to limitthe output from each of said channels;'and

. second circuit means adapted to receive the outputs from said firstcircuit means and provide therefrom a net signal to be applied to theexposure control means.

1. For use in a camera having exposure control means, circuitryoperative to establish a control signal for the exposure control means,comprising: a. light responsive means including a plurality ofindividual segments adapted to receive light from respective portions ofa scene to be photographed, each of the segments of said lightresponsive means having an electrical parameter which varies inaccordance with the intensity of light incident thereon; b. firstcircuit means containing a plurality of amplifiers, one for each of saidsegments of said light responsive means, including means for connectingthe output of each of said segments to a respective one of saidplurality of amplifiers; c. means for deriving a reference signalrelated in value to the total scene illustration received by said lightresponsive means; and d. means for applying a portion of said referencesignal to each of said channels, operative thereby to selectively limitthe output from each of said amplifiers.
 1. For use in a camera havingexposure control means, circuitry operative to establish a controlsignal for the exposure control means, comprising: a. light responsivemeans including a plurality of individual segments adapted to receivelight from respective portions of a scene to be photographed, each ofthe segments of said light responsive means having an electricalparameter which varies in accordance with the intensity of lightincident thereon; b. first circuit means containing a plurality ofamplifiers, one for each of said segments of said light responsivemeans, including means for connecting the output of each of saidsegments to a respective one of said plurality of amplifiers; c. meansfor deriving a reference signal related in value to the total sceneillustration received by said light responsive means; and d. means forapplying a portion of said reference signal to each of said channels,operative thereby to selectively limit the output from each of saidamplifiers.
 2. For use in a camera having exposure control means,circuitry operative to establish a control signal for the exposurecontrol means, comprising: a. light responsive means including aplurality of individual segments adapted to receive light fromrespective portions of a scene to be photographed, each of the segmentsof said light responsive means having an electrical parameter whichvaries in accordance with the intensity of light incident thereon; b.first circuit means operative to receive inputs from each of thesegments of said light responsive means and to provide an outputtherefrom as a single signal related to the sum of the individualportions; c. second circuit means containing a plurality of channels,one for each of said segments of said light responsive means; d. meansfor connecting each of said segments to a respective one of saidplurality of channels of said second circuit means; e. means forapplying a portion of the output from said first circuit means to eachof the channels of said second circuit means operative thereby toselectively limit the output from each of said channels; and f. meansadapted to receive the outputs from said second circuit means andprovide therefrom a net control signal to be applied to the exposurecontrol means.
 3. The invention according to claim 2 wherein said firstcircuit means is a summing amplifier.
 4. The invention according toclaim 2 wherein the means for deriving a portion of the output from saidfirst circuit means to be applied to said multichannel amplifiercomprises first and second resistors connected between the output ofsaid first circuit means and a source of reference potential, with thejunction of said first and second resistors applied to an input of saidsecond circuit means;